The present invention relates generally to network-based communication architecture. More particularly, the invention relates to providing controlled quality of service in packet-based networks through admission control.
Currently much of the Internet is designed to provide “best effort” service. The Internet Protocol (IP) is designed to deliver packets of information to an ultimate destination through any available internal links that enable delivery. The actual time it takes to deliver these packets depends on the route taken and the traffic congestion encountered en route. The original design of the Internet Protocol focused on providing ultimate delivery, with the actual time to achieve delivery being only a secondary consideration.
As the uses for the Internet have grown, and as Internet traffic has expanded geometrically, the original emphasis on delivery over timing is being challenged. With multicast applications and streaming audio and video applications growing in popularity, packet delivery time has become a central focus. Quality of Service (QoS) is a term often used to describe the degree to which a communications network provides reliability, availability, and timely throughput. Quality of service addresses issues such as transmission speed, timeliness of packet delivery, amount of jitter a network introduces into packet streams, and the probability of outright packet loss. As businesses begin to rely more and more on their Internet presence, some have expressed willingness to pay more for higher quality of service because the higher quality of service translates directly into a smoother, more responsive experience for their customers. Some Internet Service Providers thus offer different service level agreements through which they commit to provide different levels of service quality at different fee rates.
There are many proposals for improving quality of service in packet-switched networks such as the Internet. Quality of service may be improved at the individual router level by making the routers faster and more intelligent. However, this also increases system cost. Other proposals address the quality of service issue at the network model level. At the network model level, the performance of individual routers are largely ignored; focus instead shifts to the aggregate performance of all routers in the network. One popular approach is to consider the aggregate network only in terms of its outer boundary or end-to-end performance. Using such an analytical approach, the performance of the entire network, and the quality of service it provides, can be largely controlled by the behavior of the routers occupying the edge of the network (that is, the routers at the ingress and egress points).
There are several end-to-end network models for controlling quality of service (QoS) in popular use today. Among the leading models are Integrated Services (IntServ), Multi-Protocol Label Switching (MPLS), and Differentiated Services (DiffServ). IntServ supports a per flow quality of service guarantee. It employs a relatively complex architecture in which resources are reserved by means of a signaling protocol that sets up paths and reserves resources. MPLS provides another quality of service guarantee approach that focuses on packet forwarding. Packets are assigned labels at the ingress of an MPLS-compatible domain. Subsequent classification, forwarding, and services for the packets are then based on those labels.
Models such as IntServ and MPLS address QoS on a per connection basis and can present scalability difficulties. To provide better scalability, other models have been proposed that address QoS on a traffic aggregate basis. DiffServ is one example of such a model. DiffServ provides quality of service guarantees to packet aggregates by marking packets differently to create different packet classes/aggregates that are entitled to different quality of service handling.
For the most part, aggregate traffic-based network models share a number of common concepts. They begin from a premise that the network can be characterized as having edge and core routers. The edge routers accept customer traffic (i.e., packets from any source outside the network). The core routers provide transit packet forwarding services among other core routers and/or edge routers. The edge routers control ingress of traffic and thus perform an important admission control function, by permitting or declining requests by outside traffic to enter the network. With the ultimate traffic flow being controlled by the edge routers through admission control, the core routers simply need to differentiate traffic insofar as necessary to cope with transient congestion within the network itself. The network models may employ statistical multiplexing to maximize utilization of the core router resources.
Predicting and controlling traffic flow through a network at an aggregate level is a very complex problem. Admission control algorithms that overly restrict ingress waste internal core router resources. On the other hand, admission control algorithms that are too lax can flood the network with too much traffic, resulting in severe drops in quality of service. Numerous admission control algorithms have been proposed and while some have been quite ingenious, there remains a great deal of room for improvement.
For example, Centinkaya and Knightly, in an article entitled “Egress Admission Control,” IEEE Info. Comm. 2000, describe a framework for scalable quality of service provisioning in which admission control decisions are made at the egress routers based solely on aggregate measurements obtained at the egress router. They introduce a measurement-based service envelope as a way to adaptively describe the end-to-end service received by a traffic class.
For a more complete understanding of the invention, its objects and advantages, refer to the following description and to the accompanying drawings.